they are talking about that will increase power. I know on the turbine side, if you increase the clearance between the turbine blades and the turbine housing tunnel, you will get less back pressure and more top end power. But you will also lose responses as well. There is always a trade off. That is what I had done to my turbine housings. Increased it by .014 . The Porches guys do this and it is suppose to increase HP by 50 on the top end. Similar to increasing A/R on the turbine housing.